1. Field of the Invention
The present general inventive concept relates to a stereo sound reproduction system, and more particularly, to a method and apparatus to reproduce stereo sound, which generates optimal stereo sound designed for individual auditory properties.
2. Description of the Related Art
In general, a virtual sound generation system provides a surround sound effect such as a 5.1 channel system, using only two speakers.
Technology related to this virtual sound generation is disclosed in WO 99/49574 (PCT/AU 99/00002, filed on 6 Jan. 1999, entitled, “Audio Signal Processing Method and Apparatus”).
In a conventional virtual sound generation system, a multi-channel audio signal is down-mixed as a 2-channel audio signal using a head-related transfer function (HRTF).
Referring to FIG. 1, a 5.1-channel audio signal is input. A5.1-channel system includes a left front channel, a right front channel, a center front channel, a left surround channel, a right surround channel, and a low frequency effect (LFE) channel. Left and right impulse response functions are applied to the respective channels. Thus, a corresponding left front impulse response function 4 is convolved with a left front signal 3 with respect to a left front channel 2 in an adder 6. The left front impulse response function 4 uses an HRTF as an impulse response to be received by a left ear of a listener. An output signal 7 is combined with a left channel signal 10 to be used by a headphone. Similarly, a corresponding impulse response function 5 with respect to a right ear for a right channel speaker is convolved with a left front signal 3 in an adder 8 so as to generate an output signal 9 to be combined with a right channel signal 11. Thus, the arrangement of FIG. 1 requires about 12 convolution steps with respect to 5.1-channel signals. As such, the 5.1-channel signals are down-mixed by combining measured HRTFs. Even though the 5.1-channel signals are reproduced as 2-channel signals, a surround effect as reproduced by a multi-channel system can be obtained.
Meanwhile, the conventional virtual sound generation system does not reflect individual auditory characteristics but uses the HRTF that standardizes human auditory properties such as by using a dummy head. However, since human spatial perception of a sound source depends on each individual, the conventional virtual sound generation system that uses the standardized HRTF fails to produce the best stereo sound performance.